As shown in FIG. 1, an electrically-driven jogging machine 10 of the prior art comprises a frame 11 and a jogging platform 12. The frame 11 is formed of a base 11a and two support rods 11b extending uprightly from the base 11a. A control device 11c is mounted on the top ends of the two support rods 11b. The jogging platform 12 has a front side 12a which is mounted pivotally on two rotary shafts 12b which are fastened with the support rods 11b. The jogging platform 12 is provided in the underside thereof with two legs 12c making contact with the floor surface. The jogging platform 12 is provided between a left longitudinal side 12e thereof and a right longitudinal side 12f thereof with a track 12g on which an exerciser is engaged in a trotting motion imitative of jogging. The jogging machine 10 can be folded such that the rear end 12i of the jogging platform 12 is raised to rest against the support rods 11b.
In order to prevent the interference between the frame 11 and the jogging platform 12 at the time when the jogging platform 12 is turned in relation to the frame 11 so as to fold the jogging machine 10, the rotary shafts 12b are located over the floor surface by a distance H which is greater than a distane S between the rotary shafts 12b and the edge of the front side 12a of the jogging platform 12. As a result, the track 12g is slanted in relation to the floor surface at the time when the jogging machine 10 is in a normal operating state, as shown in FIG. 1. In the event that an exerciser wants to do a horizontal jogging, the legs 12c of the jogging platform 12 must be so adjusted as to be flush with the rotary shafts 12b. As a result of the adjustment of the legs 12c, the center of gravity of the prior art jogging machine 10 is so raised as to undermine the stability of the machine 10 in operation. In addition, the adjustment of the legs 12c is done manually.